Field of the Invention
The present invention generally relates to pumps, which could be in various configurations, such as in the form of rotodynamic or centrifugal pumps, or positive-displacement pumps, and which may be magnetically driven or may have dynamic seals.
Description of the Related Art
Many pumps utilize dynamic seals, which are mechanical seals between rotating parts. However, in some pumping applications, it is desirable to try to avoid potential seal leakage by not using seals in conjunction with rotating parts. Accordingly, in some instances, it is becoming more common in the pump arts to employ a magnetic drive system to eliminate the need for seals along rotating surfaces. The present disclosure addresses numerous shortcomings in prior art equipment, such as pumps, some of which utilize a magnetic coupling, while others of which may be employed with pumps having seals along rotating surfaces. The pumps also may employ rotodynamic or positive-displacement pumping principles. The following are several of the shortcomings recognized and sought to be addressed in the present disclosure.
Prior art systems for supporting a rotor assembly within a magnetically driven pump may be of different constructions but tend to provide radial and axial (thrust) bearing support for the rotor assembly that does not rely on the canister that separates the fluid pumping chamber from the drive portion of the pump. This results in a disadvantage of causing magnetically driven pumps to have greater axial length and weight, because the bearing support is located forward and/or rearward of the pumping portion of the rotor assembly. For example, bearings providing radial support and forward and rearward thrust or axial bearings that restrict forward or rearward motion typically are located forward and/or rearward of the pumping elements of a rotor assembly.
Almost all magnetically coupled pumps have a recirculation path that allows a small percentage of the pump fluid flow to recirculate from the pump outlet or discharge side, back to the inlet or suction side. This recirculation is used mostly for lubrication and cooling of bushings and for cooling of the canister, which may get hot due to electrical eddy currents generated by the magnetic coupling. Prior art recirculation paths include one or more segments where the path is essentially a hole thru a single part, such as a hole thru a single stationary part of the pump casing or thru a single piece rotating impeller. The downside of a hole thru a single part is that it is prone to causing clogging of the recirculation path.
In the chemical processing industry, the standard ASME B73.1 is a very popular specification for most centrifugal dynamically sealed pumps. In this standard and in the ISO 5199 standard, one of the main features of the specification is the establishment of a common mounting footprint, including the sizes and locations of the outlet or discharge port, the inlet port, the mounting foot and the shaft of the pump. The industry also sells magnetically coupled pumps but they utilize a different rear end mechanical drive portion or power end in comparison to the dynamically sealed pumps. There are far fewer magnetically coupled pumps, so the power ends for magnetically driven pumps tend to be more costly. Also, due to overall size and especially axial length, no magnetically coupled pumps known to the inventors have been able to utilize the power end that is commonly used with the dynamically sealed pumps while meeting either of the standards for the location of the stated features involved in mounting such pumps.
When a rotor assembly of a pump includes an impeller, the pump generally is most efficient and has the best suction capability when the center starting ends of the vanes have a relatively small diameter. However, in a magnetically driven rotodynamic pump, a front nose cap that holds a front axial bearing is most beneficial if it has a relatively large outer diameter, so that the axial bearing can be large. In a typical design, a nose cap must be assembled from the front of the impeller, so the center of the forward ends of the impeller vanes must start at a diameter at least as large as the diameter of the nose cap. This requires a disadvantageous tradeoff pitting a desired small diameter for the front end of the impeller vanes against a desired large diameter of a front axial bearing.
As noted above, it is common for pumps to have separate radial and axial bushings or bearings. This tends to add undesirable complexity and length to a pump.
The above are some of the shortcomings of prior art pumps that are sought to be addressed by the teachings and examples provided in the present disclosure.